This invention relates to earth connections to workpieces and is particularly but not necessarily exclusively concerned with a workpiece to which an arc is to be struck during arc processes suth as cutting or welding.
In open air and relatively dry conditions and with an arc process effected on a workpiece the voltage at the workplace can be raised, and if a circumstance arose where the workpiece was not effectively earthed and the operative does connect to earth, then an electric shock can be caused to the operative at a level that is uncomfortable. This problem is exacerbated when using arc processes underwater, where it is necessary to use voltages at a level that could be hazardous to divers, and hence even more desirable to ensure that electrical connections are properly made.
This is particularly the case for connections to a workpiece which may be considered as one electrode of an arc process, which, being relatively large, may influence the potential to which the diver is exposed. It will often tend to be considered as an earth or ground and at the same potential as the diver. If this is not fully connected to the same “earth” as the diver, it could give rise to exposure of the diver to voltage when applying the arc process via the electrode of the supply. Even when the workpiece is properly connected to earth, it is necessary to ensure, when using higher current in the arc process, that the impedance of the connection is not so high as to cause the voltage on the workpiece relative to the diver to become elevated to hazardous levels. It might be noted that this hazard potential is not limited to processes used underwater.
An essential difficulty with all electrical connections, and particularly underwater, is that it is frequently impossible to be sure that the integrity of the connection is such that a workpiece is properly connected to earth and that the impedance of the connection is not such as will elevate voltage on the workpiece to hazardous levels.